Although the fine structure of malarial parasites has been studied by many investigators with the conventional electron microscope, there remain many unanswered questions. Re-examination of the morphology of the parasites by the high voltage electron microscope together with stereoscopic analysis has been rewarding for understanding of the physical relationships of various subcellular organelles. For this proposed period, we will particularly concentrate on the penetration process of the host cell by the merozoite by studying the structure of the merozoite, surface coats of the freed merozoite, and interaction between the host cell and parasite membranes under various conditions. Such studies, I believe, ultimately will lead to the discovery of better methods for interference of the parasite's infection. Also, host cell changes produced by plasmodium will be analyzed by both high voltage and conventional electron microscopy.